What about a circle for the front support? That way you you’d really only have to adjust it along a linear path, front to rear, and probably a small adjustment at that, and circular shape would engage regardless of the angle of the work piece?
I think the nice part about a front support is that it would provide and anchor to allow you to exert downward pressure in the work to insure it doesn’t lift. Probably not necessary, but added insurance. As you say, most splines aren’t aggressive cuts…although maybe dovetail splines would be considered more so.
Ryan/// ~sigh~ I blew up another bowl. Moke told me "I made the inside bigger than the outside".